Wireless access systems have been widely deployed to provide various types of communication services such as voice or data services. Generally, a wireless access system is a multiple access system capable of supporting communication with multiple users by sharing available system resources (bandwidth, transmit power, etc.). Multiple access systems include, for example, a code division multiple access (CDMA) system, a frequency division multiple access (FDMA) system, a time division multiple access (TDMA) system, an orthogonal frequency division multiple access (OFDMA) system, a single carrier frequency division multiple access (SC-FDMA) system, etc.
When an existing beamforming method applies to an mmWave system used on high frequency band, it may cause a problem that a considerably long time delay is generated from a beam searching and a problem that unique channel property of a radio channel cannot be obtained. Moreover, there is a problem that an existing ray scanning method is applicable to a system having a small cell size only.